Conventionally, one example of a function installed in a computer system is a remote copy function which copies data that has been written to a logical volume (hereinafter called the primary volume) in a certain storage apparatus (hereinafter called the primary storage apparatus) to a predetermined logical volume (hereinafter called a secondary volume) in another storage apparatus (hereinafter called the secondary storage apparatus) which is installed in a site separate from the primary storage apparatus (see PTL1).
In reality, in a computer system with this kind of remote copy function installed, a primary volume in a primary storage apparatus and a secondary volume in a secondary storage apparatus are configured as one pair (hereinafter termed a copy pair). Further, if data is written to the primary volume, the primary storage apparatus transfers this data to the secondary storage apparatus together with a write command, synchronously or asynchronously with the writing. In addition, upon receiving this write command and this data, the secondary storage apparatus writes the command and data to an address, designated in the write command, in the secondary volume.
With this remote copy function, since data is retained in duplicate in both the primary storage apparatus and secondary storage apparatus, the protection of data from natural disasters such as earthquakes, fire and flood, and terrorism can be reinforced.
Furthermore, another function installed in a computer system is an external connection function which enables a certain storage apparatus to virtualize a logical volume provided by another storage apparatus (hereinafter called an external storage apparatus) (see PTL2).
In the storage apparatus in which the external connection function is installed, a virtual logical volume (hereinafter called a virtual volume) which is provided to the host apparatus is created and this virtual volume is mapped to (associated with) a virtual target logical volume in an external storage apparatus.
Furthermore, if a first access command (read command or write command) targeting the virtual volume is supplied from the host apparatus, the storage apparatus converts the first access command to a second access command targeting the logical volume to which the virtual volume is mapped and issues a second access command to the external storage apparatus, causing the external storage apparatus to execute access processing corresponding to the first access command.
With the external connection function, logical volumes each provided by a plurality of external storage apparatuses can be centrally managed, thereby facilitating the addition of storage apparatuses.